1. Field of the Invention
The present invention relates generally to a vibration damping mount of the nature used for supporting internal combustion engines on automotive vehicle chassis and the like, and more specifically to such a mount which is filled with an electrorheopectic fluid (ERF), the viscosity of which can be controlled by via the impression of a voltage.
2. Description of the Prior Art
JP-A-57-84220 discloses a fluid filled mount which can be tuned to absorb a plurality of different frequencies. As shown in FIG. 6, this device, which is generally denoted by the letter M, comprises an essentially tubular elastomeric body 1 and upper and lower connection members 2, 3 which are securely attached to the open ends thereof. In this arrangement the lower connection member 2 is arranged to be connected to the vehicle chassis while the upper connection member 3 is adapted for connection to an engine or power unit (engine and transmission combination).
A diaphragm 4 and a dished circular separation plate 5 are sandwiched in the illustrated manner between the upper connection member 3 and an annular plate (no numeral) which is directly vulcanized or similarly permanently connected to the upper end of the tubular elastomeric body 1. With this arrangement a variable volume working chamber R1, an expansion chamber R2 and an air chamber Ro are defined within the mount.
The circular separation plate 5 is comprised of three members; an annular base plate member 6, a plug 7 which is press fitted into place within an annular flange (no numeral) which depends from the lower surface 6a (as seen in the drawings) of the base plate 6, and a disc-like valve member 8 which is retained within a chamber defined between the plug 7 and the base plate 6.
The base plate 6 and the plug 7 are formed with essentially coaxial large diameter openings 9 and 10. The diameters of these openings 9, 10 are, as shown, both less than the diameter of the valve member 8.
An orifice opening 11 is formed in the valve member 8. The chambers R1 and R2 are filled with a suitable hydraulic fluid.
With this arrangement, upon relative displacement between the engine and the chassis, the elastomeric body 1 is subject to distortion which changes the volume of the working chamber R1. Working fluid is induced to flow between the working and expansion chambers R1 and R2.
In the case the displacement amount is low and occurs at a high frequency (viz., the mount is subject to low amplitude high frequency vibration), the flow fluid back and forth between the chambers R1 and R2 is insufficient to induce vertical displacement of the valve member 8. As a result, almost no damping effect is produced and engine vibration which tends to induce discomfort of passengers in the vehicle cabin are prevented from being transferred from the engine to the vehicle chassis.
On the other hand, when the mount is subject to vibration which exhibits a large amplitude and a low frequency, the amount of fluid which is displaced between the chambers R1 and R2 increases to a high level and the valve member 8 is induced to move up and down within the chamber in which it is confined. Upon being induced to rise into contact with the lower surface 6a and the base plate 6, the fluid which is displaced from chamber R1 is forced to pass through the orifice opening 11 into chamber R2. Conversely, when the valve member 8 is brought into contact with the plug 7, by the flow of fluid from the expansion chamber R2 back into the main working chamber R1 due to expansion of the latter, the fluid which is flowing between the chamber is forced to pass through the orifice opening 11. As a result of this, amount of force which is applied to the vehicle chassis is reduced.
However, this arrangement is such that, when the mount is subject to low amplitude low frequency vibration which tends to be generated when the engine is idling and producing vibrations in a relatively low frequency range, the pressure which develops in the main working chamber R1 is able to leak out to the expansion chamber R2 without being forced to pass through the orifice.
More specifically, when the above described type of mount is exposed to idling and engine shake type vibration in the relatively low vibration frequency zone the valve member 8 will usually be seating the lower surface 6a of the base plate 6 or the plug 7. As a result, the flow of fluid which moves between the chamber R1 and R2 passes through the orifice opening 11 and subject to a modification which dampens the transmission of vibration which tends to be transmitted to the vehicle chassis.
On the other hand, in the event of relatively high frequency vibrations which tends to cause cabin resonance noise, it is necessary to avoid the valve member 8 from being induced to contact both the lower surface 6a of the base plate 6 and the plug 7 in a manner which renders the orifice 11 active.
However, in actuality, during the application of very small vibrations which tend to be produced in the above mentioned relatively low frequency idling range, fluid tends to leak through the separation member 5 prior the valve member 8 being induced to seat on either the lower surface 6a of the base plate or the plug 7, with the result that the damping action of the orifice opening 11 is not induced during this time. Further, in the low vibration frequency range in which engine shake occurs until the valve member seats on either the lower surface 6a or the plug 7, the leakage of fluid flow also occurs and the full effect of the orifice 11 opening is not achieved and fully effective control of vibration control is not realized.
Efforts to overcome this problem have only increased the cost of the device to undesirably high levels.